1. Field of the Invention
This invention concerns a data transmission method and data transmitter that transmits data to which address information has been added, a data receiver and data reception method that receives transmission data based on address information, and a data transmission and reception system that adds address information and transmits and receives data.
2. Description of Prior Art
Wireless call systems or radio paging systems (merely referred as a radio paging system, hereinafter) that transmit information input by telephone have long been available. In a radio paging system, a so-called pager is used as an information reception terminal.
In recent years, information broadcast services have become available in which various information is provided using this radio paging system. This information broadcast service makes it possible, for example, to receive on a pager or pager terminal various information such as information about public events or weather forecast information.
A pager receives various information broadcast from various broadcast base stations based on ID information, etc. arranged in the same data frame.
As shown in FIG. 1A, in the format of the data frame used heretofore, the frame consists of 15 groups G1, G2, G3, G4, . . . , G14, G15 as data transmission cycles.
As shown in FIG. 1B, each group consists of synchronization signal 201, address/message discrimination signal 202, multiple selection call signals 203, 204, and a phase compensation signal 205. Here each frame has a period of, for example, 29 seconds.
Synchronization signal 201 is the part for synchronizing the group to which the pager corresponds and belongs and receiving the selection call signal, among said synchronized group, that is addressed to the pager.
As shown in FIG. 1C, selection call signals 203, 204 consist of address signal 211 and message signal 212, and the constituent units of both signals are, for example, error-correcting code word [BCH(31,16)] (Bose-chaud-huri-Hocquenghem code). For example, this selection call signal consists of a total of 155 bits with its content set to 31-bit units and is expressed specifically with an address signal of 61 bits and a message signal of 93 bits.
Address/message discrimination signal 202 shows in code word units how address signal 211 and message signal 212 are lined up within the selection call signal. This allows the pager to efficiently retrieve address signal 211 alone.
Address signal 211 is set to the address that identifies the pager. The address signal 211 consists of unique call numbers that correspond to each pager. The pager distinguishes this address signal 211, and if it confirms that it is its own address signal (hereafter called its self-address), it sounds a tone, decodes the message signal, and displays the content. The self-address is set to be variable.
Phase compensation signal 205 is a signal that is used on the base station side to cause the phase of transmission signals to match between broadcast base stations.
The pager belongs to some one group within the frame, is synchronized by receiving the synchronization signal of the group to which it belongs, and receives a selection call signal within its group. Then, if its self-address is present within the received selection call signal, the pager sounds a tone and displays the content of the message signal.
The address of a pager has been limited physically to a relative small number, such as a maximum of 8. Because of this, the types of information the pager can receive is limited by the number of its self-addresses, making it difficult to handle a wider variety of information.
Different information can be received by rewriting the self-address, but, as may be expected, the number that can be received simultaneously is limited by the number of self-addresses, and if the number of items of information to be received is greater than the number of self-addresses, it becomes necessary to rewrite the self-address frequently. But it is generally not easy or realistic to rewrite the self-address.
Thus the purpose of this invention, which was devised in consideration of the above situation, is to provide a data transmission method and data transmitter, data receiver and data reception method, and data transmission and reception system that make it possible to transmit and receive more types of information without changing the existing communication system.